Currently, air-filter devices for the above-mentioned vehicles generally comprise, basically, on the one hand, a casing, in one or more parts, defining a volume or so-called clean compartment receiving the filtered gases and a volume or so-called dirty compartment receiving the gases to be filtered, and, on the other hand, a filtering body separating the two above-mentioned compartments, installed in an intermediate mounting area or compartment and having a peripheral seal that comes to be applied against an edge or circumferential similar internal step of the casing, which delimits the said intermediate compartment in relation to the clean compartment.
The peripheral seal is usually insert-moulded round the external edge of the said filtering body or consists of a band area at the edges of the said filtering body.
One of the existing major concerns in the development of these air-filter devices is to optimise, in terms of accessibility, operational comfort and reliability, the operations involved in changing the filtering body at regular intervals.
To meet this demand, an air-filter device has been proposed, notably in document DE-A-2512724, in which the filtering body is made as an insert fitted with a frame, capable of being introduced and extracted by simple sliding, in the manner of a drawer, into an adapted intermediate compartment, provided with an adapted side access opening.
Tightness in the mounted condition is obtained by compressing the peripheral seal, during the introduction movement, against a circumferential application surface formed on the internal face of the casing. This compression movement is generated by sliding the bevelled or inclined sides of the frame upon surfaces of the opposite inclination present on the internal face of the casing.
However, in this construction, the seal risks being damaged and/or incorrectly positioned taking into account its displacement under pressure in relation to the casing.
In an attempt to overcome this drawback, it has been proposed, notably in document EP 0 391 019, to have a first supporting body receiving the filtering body and a second compression body designed to co-operate mechanically with the supporting body at the respective contact surfaces coming to bear in mutual sliding, the two above-mentioned bodies having structures in the form of frames and being mounted in the manner of sliding drawers in the intermediate compartment, the latter having a side access opening made in the casing to introduce and extract the filtering body/supporting body assembly, as well as any compression body, by sliding in respective opposite directions.
This compression body is also guided in sliding bearing along a second edge or similar circumferential internal step of the casing, delimiting the said intermediate compartment in relation to the dirty compartment, and may be moved selectively between a slackening off or release position or range of slackening off or release positions in which the seal of the filtering body is not compressed and a position of forced stress in which the filtering body is locked in position and its seal compressed, under the action of a control device that can be maneuvered from outside the casing and connected or built into a cover or cap designed to block off the side access opening.
Now, the contact surfaces in mutual sliding bearing, formed on the two opposite side parts of the frames of the supporting and compressing bodies forming the sides which extend in the opposite sliding directions possible for the said bodies, are shaped so as to have the opposite inclinations in relation to the said opposite sliding directions, so that a relative sliding between the said two bodies in one of the said directions results in an increase or release of compression by the supporting body of the seal of the filtering body.
Nevertheless, both of the above-mentioned constructions of air-filter have one major drawback, namely that sealing by compression is achieved by pushing in the direction of introduction of the filtering body, this push being transmitted, chiefly at the end of the introduction movement, when the force of the push and often the inertia of movement are at their maximum, to the casing and by the latter to its fixing points and to the parts that are connected to it.
The stress transmitted to the surroundings of the casing can have an intensity such as to generate clearances, even causing ruptures or breaks, at the interfaces where the efforts concerned are resumed, particularly in the event of pronounced friction (binding, jamming and fouling).
Moreover, the above-mentioned pushing movement is made by the operator without any control, except for the end-of-travel stop, in one go or a plurality of goes.